Amethyst is one of the most precious and valuable stones belonging to the quartz group of minerals, with exception to rare blue-green gem silica. It is recognized as the official birthstone for the month of February.
Amethyst belongs to the macrocrystalline branch of quartz and owes its violet/purple color to iron and aluminum impurities. Without such coloring agents, amethyst would simply be transparent, ordinary colorless quartz.
Like other varieties of macrocrystalline quartz, amethyst has transparent to translucent clarity and a vitreous luster. Cryptocrystalline varieties of quartz almost always occur with translucent to opaque clarity.